In a fuel cell that operates without discharging fuel gas that is in the fuel cell (such as the fuel cell disclosed in JP(A) 9-312167, for example), the electrode catalyst becomes covered with impurities such as nitrogen and moisture that accumulate in the fuel cell as time passes when the fuel cell is operating. As a result, electromotive reaction in the electrode catalyst is impaired, resulting in a decrease in output voltage.
To combat this problem, in a fuel cell of related art that operates without discharging fuel gas that is in the fuel cell, when the output voltage becomes equal to, or less than, a predetermined reference voltage, anode exhaust gas containing impurities (on the anode side) in the fuel cell is discharged outside the fuel cell in an attempt to recover the output voltage.
In the fuel cell of the related art that operates without discharging fuel gas that is in the fuel cell, however, there is almost no flow or diffusion of fuel gas particularly at the ends of each cell in the fuel cell stack so impurities tend to accumulate there, making it difficult to generate sufficient power. As a result, the output voltage of the fuel cell frequently drops so unless the impurities that accumulate in the fuel cell are discharged more frequently, the necessary output voltage is unable to be obtained. In this case, because fuel gas in the fuel cell is also discharged when the impurities are discharged, the fuel efficiency performance of the fuel cell decreases.